The invention discloses a preparation method of a small-pore-
diameter narrow-distribution 
polytetrafluoroethylene microporous membrane. By mixing of dispersible 
polytetrafluoroethylene resin, solventoil and a surface 
active agent and adopting the processes of 
ageing, blank manufacture, pushing and squeezing, calendaring, oil removal, longitudinal pulling treatment, horizontal pulling treatment, 
sintering and 
sizing and the like, the 
polytetrafluoroethylene microporous membrane with the 
pore diameter being 10-50nm and the bubble-point 
pore diameter being less than 80nm is manufactured; the surface 
active agent is added into a formula, and by the action of the surface 
active agent, the wettability of the 
solvent oil is obviously improved, and the wrapping degree of the 
solvent oil to the polytetrafluoroethylene resin is obviously improved, so that the formation degree of micropores in the drawing and expanding processes is greatly reduced; under the action of same shearing force, the formed micropores are more and smaller, so that the microporous membrane with small 
pore diameter and narrow distribution is obtained; the preparation method is easy in industrial production, can utilize the existing 
manure equipment only in need of proper process adjustment, and has strong practicability and wide applicability.